1. Field of the Invention
This invention relates generally to computer hard disk drives and, more particularly, to improvements to the rotary actuator of hard disk drives for better dynamic performance.
2. Description of Related Art
Moving magnetic storage devices, especially magnetic disk drives, are the memory devices of choice. This is due to their expanded non-volatile memory storage capability combined with a relatively low cost.
Magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer in proximity to the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or a write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air-bearing, generated by the rotating disk.
Alternatively, the transducer may operate in contact with the surface of the disk. Thus the suspension provides desired slider loading and dimensional stability between the slider and an actuator positioner arm which couples the transducer/slider/suspension assembly to the actuator. The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single positioner arm extending from a pivot point, or alternatively a plurality of positioner arms arranged in a comb-like fashion extending from a pivot point. A rotary voice coil motor (VCM) is attached to the rear portion of the actuator assembly to power movement of the actuator over the disks.
The VCM located at the rear portion of the actuator assembly is comprised of a top plate spaced above a bottom plate with a magnet or pair of magnets therebetween. The VCM further includes an electrically conductive coil disposed within the rearward extension of the actuator assembly and between the top and bottom plates, while overlying the magnet in a plane parallel to the magnet. In operation, current passes through the coil and interacts with the magnetic field of the magnet so as to rotate the actuator assembly around its pivot and thus positioning the transducer as desired.
The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks.
During operation of the disk drive, the actuator, driven by the VCM, is positioned radially over the disk surface under the control of a positioning servo system. The servo system is designed to accurately position the read/write transducer over a selected data track on the disk in as short a time as possible. The actuators of most disk drive systems have at least two positioner arms, an outer upper positioner arm (outer upper arm) and an outer lower positioner arm (outer lower arm) so that data may be written to and read from both surfaces of the disk. Disk drive systems having more than one disk have actuators with one or two outer arms and at least one inner positioner arm (inner arm). The outer arms each support a single suspension and corresponding slider/transducer assembly. The inner arms each support two suspensions with their slider/transducer assemblies, the suspensions being mounted in a back-to-back configuration on each side of the positioner arm.
Actuator positioner arms have resonant frequencies that can adversely affect the performance of the servo system. The dynamics of the upper outer arm and the lower outer arm are typically different than the dynamics of the inner arms due to the fact that the outer arms generally support one suspension and the inner arms support two suspensions. The different dynamics of the outer and inner arms leads to additional modes of vibration on the actuator that can degrade performance of the disk drive system.
It therefore can be seen that there is a need for an actuator that has outer and inner arms with closely matched dynamics to the inner arms to reduce the modes of vibration on the actuator that can adversely affect the performance of the disk drive.